Photocatalysts are excited when irradiated with light of wavelength having an energy higher than the band gap to exhibit strong catalytic activity. Particularly, they are high in oxidation power and decomposition power for organic materials or a part of inorganic materials such as NOx, and a light which is low in cost and very small in environmental load can be utilized as an energy source. Therefore, application of the photocatalysts to environmental purification, deodorization, anti-pollution, and sterilization has recently been made intensively. Moreover, it has been found that when photocatalysts are excited, the surface thereof becomes hydrophilic, resulting in reduction of contact angle with water, and utilizing this action, application to inhibition of fogging and pollution has also been conducted. As the photocatalysts, there are generally used metallic compounds such as oxides and sulfides, particularly, fine particles of titanium oxide and zinc oxide having high photocatalytic activity. However, since wavelength of excitation light for titanium oxide or zinc oxide is in the ultraviolet region of 400 nm or less, special light sources such as ultraviolet lamp are necessary, and field of utilization is limited. Therefore, a technology of exhibiting photocatalytic activity under irradiation with visible light by doping titanium oxide with different elements such as nitrogen, sulfur and carbon has been proposed, and there is known, for example, a method of obtaining a nitrogen-doping type visible light-responsive photocatalyst titanium oxide by reacting an amorphous titanium oxysulfate with a nitrogen-containing compound such as an urea compound or an amine compound, and then firing the reaction product (Patent Document 1). There are also known technologies to give photocatalytic activity under irradiation with visible light by supporting a halogenated platinum compound on the surface of titanium oxide particles (Patent Document 2) or supporting a halogenated platinum compound on titanium oxide particles having anisotropic shapes such as spindle-like, rod-like and acicular shapes (Patent Document 3).
Patent Document 1: JP-A-2002-29750
Patent Document 2: JP-A-2002-239395
Patent Document 3: JP-A-2004-73910